Implantable medical devices, such as implantable cardiac devices, are devices which are implanted in the body of a patient and are capable of monitoring the function of a patient's organ, such as their heart or brain, and are further configured in some instances to be able to deliver therapeutic electrical stimulation to the patient's organ.
Implantable cardiac devices, such as pacemakers and implantable cardioverter defibrillators (ICDs), are very commonly used implantable mechanical devices and are used to treat various heart conditions. These types of implantable cardiac devices typically have one or more leads that are positioned adjacent the walls of the heart and a control unit which receives signals indicative of the functioning of the heart. The control unit induces the delivery of therapeutic electrical stimulation to the walls of the heart via the leads in response to sensed heart conditions. Generally, the control unit incorporates a processor that is capable of recognizing and discerning particular heart irregularities based upon the signals that the processor receives. The implanted leads act as a sensor which delivers an intracardial electrogram (IEGM) to the processor, which provides the processor with a signal that is indicative of the heart function. Hence, the processors of these types of implantable cardiac devices continuously receive an IEGM signal that allows the processor to determine whether therapeutic stimulation of the heart is needed to regulate the heart function.
Generally, the IEGM signal that is provided by the lead is initially sampled by the sensor at a fairly wide bandwidth which results in a broad spectrum signal indicative of the function of the heart. However, this cardiac rate sensing IEGM signal is typically filtered so that the processor receives a narrower bandwidth signal which can be used by the processor to detect thresholds for delivering therapeutic electrical stimulation. In one application, the narrow band signal provides the processor with a signal that is indicative of the R wave and the T wave is filtered out of the signal so that the processor can get an accurate determination of the intrinsic heart rate of the patient.
Typically, the bandwidth of the IEGM signal that is used by the processor as a heart rate sensor input, is selected to be narrower than the bandwidth of the original IEGM signal. For example, in current generation pacemakers manufactured by PACESETTER, INC. of Sylmar, Calif., the bandwidth of the IEGM signal provided by the implanted leads can be between 1 and 100 Hz. However, the filtered electrogram that is provided to the processor on a sense channel input is on the order of 10 to 60 Hz for an ICD 20 to 120 Hz in the pacemaker. The narrower bandwidth signal results in the processor receiving a signal where more components of interest, such as R waves, are more clearly defined, thereby allowing these more clearly defined events to serve as the markers or thresholds for initiating or altering the delivery of pacing, cardioversion or defibrillation therapy.
Hence, these types of implantable cardiac devices essentially develop two or more IEGM signals: a broadband signal from the sensing electrode and narrow band signals that are used by the processor as sense inputs. One problem that arises as the result of the implantable cardiac device effectively generating two or more IEGM signals is that the physicians who are implanting the devices and who are also subsequently reviewing the operation of the device may alternatively desire to see either the regular broad band IEGM signal or the narrow band IEGM signal provided to the processor on the sense channel.
Specifically, most implanted cardiac devices that are used today are capable of storing IEGM signals so that these signals can be subsequently transmitted to a physician for the physician to review on an external programmer. Typically, the external programmer communicates with the implanted device via an RF communications link. When a particular heart episode that necessitates the delivery of corrective stimulation by the implanted cardiac device occurs, the device also initiates a recording process whereby an IEGM signal is recorded in memory for subsequent evaluation. Stored IEGM signals can be transmitted from the memory of the implanted device to the external programmer and then displayed to the physician on a display that is associated with the external programmer. This information can be used by the treating physician to ascertain whether the device is correcting heart function appropriately and can also be used as a diagnostic tool for assessing the progression of the patient's heart disease and for setting sensing detection parameters.
In another application, the treating physician may view the IEGM signal, either at implantation or during a follow up visit, in real time. In these applications, some physicians may want to view the broad band IEGM signal and other physicians may only want to see the narrow band signal that is being provided to the processor. For example, the physician may want to assess the performance of the sensor in obtaining the IEGM signal using the broad band sensor input signal. Alternatively, some physicians may want to view the narrow band signal being provided to the processor to ensure that the filtering of the broad band signal results in an appropriate signal being provided to the processor.
Hence, some physicians will want to see the full bandwidth electrogram signal so as to get a better picture of the heart's function. Other physicians may simply want to look at the narrow band electrogram signal that is being provided to the implanted device on the sense channel so that the physician can review the electrogram signal that is indicative of the cardiac intrinsic rate or device function.
As a result of the competing desires of physicians, many implantable cardiac devices have incorporated multiplexers that receive both the broad band electrogram signal from the leads and also the filtered narrow band sense electrogram signal. These systems typically store only the signal that is selected by the treating physician as the signal to be stored. Subsequently, when a physician wishes to review the electrogram signal, the signal is then provided via the telemetry circuit to the external programmer. Hence, in the typical prior art, implanted cardiac devices must incorporate additional circuitry and control lines so as to be able to store in the memory either the broad band electrogram signal or the narrow band sense electrogram signal. This additional circuitry and control lines occupies limited space within the control unit of the cardiac device and further consumes limited power that is provided by the battery, thereby shortening the life of the implanted cardiac device. If the narrow and broad band signals are stores, the storage time is reduced by half.
Moreover, with most implanted cardiac devices, once the treating physician has selected which of the electrogram signals they wish to have stored, the other electrogram signal cannot be seen by the treating physician as it was not stored in the memory of the implanted cardiac device. This lack of flexibility is, of course, compounded by the fact that the physician who makes the initial selection as to which electrogram is to be stored may not be the same physician who will be subsequently reviewing the stored electrogram for follow up treatment of the patient and to follow-up on the performance of the implanted cardiac device.
Hence, there is a need for an implantable cardiac system which is capable of allowing a treating physician to subsequently view recorded electrograms of heart events having different bandwidths via an external programmer without requiring additional components and circuitry to be implanted in the body of the patient. To this end, there is a need for an external programmer that is adapted to provide the physician with either the wide band electrogram or the narrow band sense channel electrogram signal.